Spring MVC

SpringMVC中扮演关键角色的DispatcherServlet类。

1 DispatcherServlet

1.1DispatcherServlet 类图

1.2 初始准备阶段

1.2.1 init（）

HttpServletBean类中init（）方法

public final void init() throws ServletException {if (this.logger.isDebugEnabled()) {this.logger.debug("Initializing servlet '" + this.getServletName() + "'");}try {PropertyValues pvs = new HttpServletBean.ServletConfigPropertyValues(this.getServletConfig(), this.requiredProperties);BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);ResourceLoader resourceLoader = new ServletContextResourceLoader(this.getServletContext());bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, this.getEnvironment()));this.initBeanWrapper(bw);bw.setPropertyValues(pvs, true);} catch (BeansException var4) {this.logger.error("Failed to set bean properties on servlet '" + this.getServletName() + "'", var4);throw var4;} this.initServletBean();if (this.logger.isDebugEnabled()) {this.logger.debug("Servlet '" + this.getServletName() + "' configured successfully");} }

DispatcherServlet的初始化过程主要是通过当前的servlet类型实例转换为BeanWrapper类型实例，

以便使用Spring中提供的注入功能进行对应属性的注入。如ContextAttribute、contextClass、 namespace\

contextConfigLocation等，都可以在web.xml文件中以初始化参数的方式配置在servlet的声明中。

1.2.2 initServletBean（）

 FrameworkServlet的initServletBean（）

this.webApplicationContext = this.initWebApplicationContext();this.initFrameworkServlet();

this.webApplicationContext = this.initWebApplicationContext();this.initFrameworkServlet();protected WebApplicationContext initWebApplicationContext() {//从ServletContext中获得根容器WebApplicationContext rootContext = WebApplicationContextUtils.getWebApplicationContext(this.getServletContext());WebApplicationContext wac = null;if (this.webApplicationContext != null) {wac = this.webApplicationContext;if (wac instanceof ConfigurableWebApplicationContext) {ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext)wac;if (!cwac.isActive()) {if (cwac.getParent() == null) {cwac.setParent(rootContext);} this.configureAndRefreshWebApplicationContext(cwac);}}} if (wac == null) {wac = this.findWebApplicationContext();} if (wac == null) {wac = this.createWebApplicationContext(rootContext);} if (!this.refreshEventReceived) {this.onRefresh(wac);} if (this.publishContext) {String attrName = this.getServletContextAttributeName();this.getServletContext().setAttribute(attrName, wac);if (this.logger.isDebugEnabled()) {this.logger.debug("Published WebApplicationContext of servlet '" + this.getServletName() + "' as ServletContext attribute with name [" + attrName + "]");}} return wac;}

createWebApplicationContext ()以根容器为父容器创建新的容器，所以在新创建的容器中找不到的bean可以在根容器中找到。

1.2.3 onRefresh()

protected void onRefresh(ApplicationContext context) {this.initStrategies(context);}protected void initStrategies(ApplicationContext context) {this.initMultipartResolver(context);this.initLocaleResolver(context);this.initThemeResolver(context);this.initHandlerMappings(context);this.initHandlerMappings(context);this.initHandlerExceptionResolvers(context);this.initRequestToViewNameTranslator(context);this.initViewResolvers(context);this.initFlashMapManager(context);}

这里就是DispatherServlet初始化的地方。其中我们重点关注

initHandlerMappings()、 initHandlerMappings（);

以initHandlerMappings（）为例，主要是从容器中获得类类型为HandlerMapping.class的bean并存储在list中。如果找不到则获取DispatchServlet.properties文件中默认的两个HandMapping.

# Default implementation classes for DispatcherServlet's strategy interfaces.# Used as fallback when no matching beans are found in the DispatcherServlet context.# Not meant to be customized by application developers.org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolverorg.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolverorg.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMappingorg.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\    org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapterorg.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver,\    org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\    org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolverorg.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslatororg.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolverorg.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager

static {try {ClassPathResource resource = new ClassPathResource("DispatcherServlet.properties", DispatcherServlet.class);defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);} catch (IOException var1) {throw new IllegalStateException("Could not load 'DispatcherServlet.properties': " + var1.getMessage());}}

private void initHandlerMappings(ApplicationContext context) {this.handlerMappings = null;if (this.detectAllHandlerMappings) {Map
       
         matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);if (!matchingBeans.isEmpty()) {this.handlerMappings = new ArrayList(matchingBeans.values());AnnotationAwareOrderComparator.sort(this.handlerMappings);}} else {try {HandlerMapping hm = (HandlerMapping)context.getBean("handlerMapping", HandlerMapping.class);this.handlerMappings = Collections.singletonList(hm);} catch (NoSuchBeanDefinitionException var3) {;}} if (this.handlerMappings == null) {this.handlerMappings = this.getDefaultStrategies(context, HandlerMapping.class);if (this.logger.isDebugEnabled()) {this.logger.debug("No HandlerMappings found in servlet '" + this.getServletName() + "': using default");}} }
       

1.3功能实现

一句话概括流程：根据request对象获得对应的handler,然后得到对应view，最后对view进行渲染。

DispatcherServlet中doService()、doDispatch().

1.3.1 doDispatch(）

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {HttpServletRequest processedRequest = request;HandlerExecutionChain mappedHandler = null;boolean multipartRequestParsed = false; WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); try {ModelAndView mv = null;Exception dispatchException = null; try {processedRequest = checkMultipart(request);multipartRequestParsed = (processedRequest != request); // Determine handler for the current request.mappedHandler = getHandler(processedRequest);if (mappedHandler == null || mappedHandler.getHandler() == null) {noHandlerFound(processedRequest, response);return;} // Determine handler adapter for the current request.HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler()); // Process last-modified header, if supported by the handler.String method = request.getMethod();boolean isGet = "GET".equals(method);if (isGet || "HEAD".equals(method)) {long lastModified = ha.getLastModified(request, mappedHandler.getHandler());if (logger.isDebugEnabled()) {logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);}if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {return;}} if (!mappedHandler.applyPreHandle(processedRequest, response)) {return;} // Actually invoke the handler.mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); if (asyncManager.isConcurrentHandlingStarted()) {return;} applyDefaultViewName(processedRequest, mv);mappedHandler.applyPostHandle(processedRequest, response, mv);}catch (Exception ex) {dispatchException = ex;}catch (Throwable err) {// As of 4.3, we're processing Errors thrown from handler methods as well,// making them available for @ExceptionHandler methods and other scenarios.dispatchException = new NestedServletException("Handler dispatch failed", err);}processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);}catch (Exception ex) {triggerAfterCompletion(processedRequest, response, mappedHandler, ex);}catch (Throwable err) {triggerAfterCompletion(processedRequest, response, mappedHandler,new NestedServletException("Handler processing failed", err));}finally {if (asyncManager.isConcurrentHandlingStarted()) {// Instead of postHandle and afterCompletionif (mappedHandler != null) {mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);}}else {// Clean up any resources used by a multipart request.if (multipartRequestParsed) {cleanupMultipart(processedRequest);}}}}

1.3.1.1 getHandler()

完成URL与Handlerd的映射关系。

protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {for (HandlerMapping hm : this.handlerMappings) {if (logger.isTraceEnabled()) {logger.trace("Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");}HandlerExecutionChain handler = hm.getHandler(request);if (handler != null) {return handler;}}return null;}

 

简单理解从request中获得url，使用HandlerMapping获得HandlerExecutionChain，注意，这个执行链中包括了HandlerInterceptor和handler。

HandlerInterceptor接口

如同拦截器一般，依次执行上述方法。

1.3.1.2 getHandlerAdapter

protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {for (HandlerAdapter ha : this.handlerAdapters) {if (logger.isTraceEnabled()) {logger.trace("Testing handler adapter [" + ha + "]");}if (ha.supports(handler)) {return ha;}}throw new ServletException("No adapter for handler [" + handler +"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");}

getHandlerAdapter方法,如同名字一样，获得handler的适配器，handler的实现多种多样，但是我们要定义一个统一的接口来使用handler，

ex:

public class HttpRequestHandlerAdapter implements HandlerAdapter {@Overridepublic boolean supports(Object handler) {return (handler instanceof HttpRequestHandler);}@Overridepublic ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)throws Exception {((HttpRequestHandler) handler).handleRequest(request, response);return null;}@Overridepublic long getLastModified(HttpServletRequest request, Object handler) {if (handler instanceof LastModified) {return ((LastModified) handler).getLastModified(request);}return -1L;}} public class SimpleControllerHandlerAdapter implements HandlerAdapter {@Overridepublic boolean supports(Object handler) {return (handler instanceof Controller);}@Overridepublic ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)throws Exception {return ((Controller) handler).handleRequest(request, response);}@Overridepublic long getLastModified(HttpServletRequest request, Object handler) {if (handler instanceof LastModified) {return ((LastModified) handler).getLastModified(request);}return -1L;}} public class SimpleServletHandlerAdapter implements HandlerAdapter {@Overridepublic boolean supports(Object handler) {return (handler instanceof Servlet);}@Overridepublic ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)throws Exception {((Servlet) handler).service(request, response);return null;}@Overridepublic long getLastModified(HttpServletRequest request, Object handler) {return -1;}}

参考资料：

《SPRING技术内幕：深入解析SPRING架构与设计原理》

《Spring源码深度解析》

《深入分析Java  Web技术内幕》